The present invention relates generally to systems for determining peak cylinder pressure in an internal combustion engine, and more specifically to such systems for estimating peak cylinder pressure as a function of one or more engine operating conditions.
When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). This problem is aggravated through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.
One known technique for reducing unwanted emissions such as NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold valve, for controllably introducing exhaust gas to the intake manifold. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.
While EGR systems of the foregoing type are generally effective in reducing unwanted emissions resulting from the combustion process, a penalty is paid thereby in the form of a resulting loss in engine efficiency and an increased concern that the engine is operating within safe operating limits. A tradeoff thus exists in typical engine control strategies between the level of NOx production and engine operating efficiency and safety, and difficulties associated with managing this tradeoff have been greatly exacerbated by the increasingly stringent requirements of government-mandated emission standards.
One of the concerns that is heightened through the use of recirculated exhaust gas is peak cylinder pressure. Because turbochargers in EGR engines typically operate at higher speeds in order to ensure positive exhaust gas flow from the exhaust manifold to the intake manifold, boost pressures tend also to be higher than in non-EGR engines. Additionally, intake manifold temperatures are typically higher in EGR engines due to the introduction of hot exhaust gas into the fresh air stream. Both of these conditions tend to increase the peak cylinder pressure, at it is accordingly desirable to at least monitor peak cylinder pressure in real-time.
The present invention provides a system for estimating engine peak cylinder pressure as a function of other engine operating conditions.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.